Methods, intermediate radio units and radio heads of base station systems for transmission of antenna carriers

ABSTRACT

Disclosed is a method performed by an IRU ( 210 ) of abase station system ( 200 ), the base station system comprising the IRU ( 210 ), a BBU ( 230 ) connected to the IRU ( 210 ), and a first RH ( 221 ) connected to the IRU ( 210 ) via a packet data network ( 240 ). The first RH ( 221 ) is arranged for wireless transmission in RF of a plurality of antenna carriers to UEs ( 250 ). The method comprises receiving, from the BBU ( 230 ), a plurality of first digital representations of the plurality of antenna carriers of the first RH ( 221 ), each first digital representation representing one antenna carrier, the plurality of first digital representations being received in a baseband frequency range, frequency multiplexing the plurality of first digital representations of the plurality of antenna carriers into a second digital representation over a first bandwidth, and transmitting the second digital representation to the first RH ( 221 ).

TECHNICAL FIELD

The present disclosure relates generally to methods, intermediate radiounits and radio heads of base station systems of wireless communicationsystems for transmission of antenna carriers.

BACKGROUND

There are today different concepts for distributing base stationfunctionality onto different nodes into a distributed base stationsystem. Basic purposes for distributing base station functionality areto improve radio coverage and to increase throughput to User Equipments,UEs, also called mobile stations. In a distributed base station system,base station functionality is typically distributed onto a base bandunit, BBU and a plurality of remote radio units, RRU, connected to theBBU.

A first prior art distributed base station systems is shown in FIG. 1a .The base station, e.g. a 3G/4G eNodeB is split into a baseband unit, BBU110 and a number of radio units, RU, 130 connected to the BBU 110. TheBBU 110 is further connected to other nodes of a wireless communicationnetwork 100 via S1-interfaces connecting to the core network and/orX2-interfaces, connecting to other base stations. A Common Public RadioInterface, CPRI, is used to fronthaul digital antenna carriers, AxC,synchronization, and O&M data downlink and uplink to the radio units,RU, 130. CPRI is specified in CPRI Specification V7.0, dated Oct. 9,2015. The RUs 130 provide digital front-end, DFE, functions and analogfront end, AFE, functions for handling the digital antenna carriers andO&M data received from the BBU 110. The DFE comprises CPRI processing,Digital Pre-Distortion, (DPD), mixing, Crest Factor Reduction, (CFR),channel and carrier filtering etc. The AFE comprises Digital toAnalog/Analog to Digital Conversion, (DAC/ADC), Power Amplification,(PA), Low Noise Amplification, (LNA), filtering, duplexing, antennainterfaces etc. In-between the BBU 110 and the RUs 130 there may be aCPRI cross multiplexing unit, CPRI Mux, 120 to multiplex and demultiplexantenna carriers between CPRI links of the BBU and CPRI links of theRUs. CPRI is a point-to-point link protocol using dedicatedtransmitter/receiver fibers per BBU-RU connection and specified fordifferent link rates. This prior art base station system relies ondirect connections between the BBU and the RU. However, there is aninterest and need to use a common packet data network for communicationbetween the BBU and the RU, in order to better utilize communicationresources. Further, the RUs need to be rather complex in order to handlethe DFE and AFE functions mentioned above. A complex RU means a ratherexpensive RU. Also, there has to be one DFE for each antenna carrier.

A second prior art distributed base station system is shown in FIG. 1b .This system differs from the system of FIG. 1a in that an Ethernet-basednetwork, i.e. a packet data network is used for the communicationbetween the BBU and the RU. The Ethernet-based network may also be e.g.a passive optical network (PON), Digital Subscriber Line (DSL) network,or an optical transport network (OTN). Data sent over the CPRI protocolis encapsulated in Layer 2 Ethernet frames and transmitted over an 802.1Ethernet network. This technology is proprietary and called Radio overEthernet, RoE. Within the Ethernet network, between the BBU 110 and theRU 130, hub nodes 140 are placed, acting as packet switches. Typically,any antenna carrier, AxC, is transmitted in its own packet flow togetherwith 1588 synchronization data and out-of-band O&M data such asConfiguration and Fault Management data. DFE and AFE functions arehandled in the RU 130. However, the RUs are still rather complex andthere has to be one DFE handling each antenna carrier.

A third prior art distributed base station system is shown in FIG. 1c .In this system, remote active radio heads, RH 160 are connected to anIntermediate Radio Unit, IRU 150 via analog point to point interfacessuch as copper cables or fiber cables. Such a system makes it possibleto cover an area such as a floor in a building with radio coverage andcapacity, and if there are already existing copper cables in thebuilding they can be reused. The BBU 110 sends the antenna carriers inbaseband over CPRI to the IRU 150 and the IRU converts the antennacarriers into a low intermediate frequency, IF, and performs digital toanalog conversion. The analog IF antenna carriers are then distributedonto the cable that leads to the correct RH 160. The RH 160 frequencyshifts the antenna carriers to RF for wireless transmission via itsantenna(s) to UEs. Due to the low complexity of the RH, the RH can bemade cost-efficient and power-efficient compared to the systems of FIG.1a and 1b . However, in the system of FIG. 1c a packet data networkcannot be used as connection between the RH and the IRU.

Consequently, it is a need of a base station system that can utilize apacket data network for communication with the RHs/RUs and that at thesame time can use a cost-efficient RH/RU.

SUMMARY

It is an object of the invention to address at least some of theproblems and issues outlined above. It is an object of embodiments ofthe invention to provide a cost-efficient and reliable base stationsystem that utilizes a packet data network for communication with theradio heads. It is another object to reduce complexity of RH/RUs whentransmitting digital data between baseband unit and radio units of abase station system. It may be possible to achieve these objects andothers by using methods, intermediate radio units, radio heads andcomputer programs as defined in the attached independent claims.

According to one aspect, a method is provided performed by an IRU of abase station system. The base station system comprises the IRU, a BBUconnected to the IRU, and a first RH connected to the IRU via a packetdata network. The first RH is arranged for wireless transmission inradio frequency, RF, of a plurality of antenna carriers to UEs, theplurality of antenna carriers being transmitted from the first RH atindividually different RFs. The method comprises receiving, from theBBU, a plurality of first digital representations of the plurality ofantenna carriers of the first RH, each first digital representationrepresenting one antenna carrier, the plurality of first digitalrepresentations being received in a baseband frequency range. The methodfurther comprises frequency multiplexing the plurality of first digitalrepresentations of the plurality of antenna carriers into a seconddigital representation over a first bandwidth, and transmitting thesecond digital representation to the first RH.

According to another aspect, a method is provided performed by an RH ofa base station system, the RH being arranged for wireless transmissionin RF of a plurality of antenna carriers to UEs. The plurality ofantenna carriers are to be transmitted from the RH at individuallydifferent RFs. The base station system comprises the RH, an IRUconnected to the RH via a packet data network, and a BBU connected tothe IRU. The method comprises receiving, from the IRU, a second digitalrepresentation in a first bandwidth, the second digital representationcomprising a plurality of first digital representations of the pluralityof antenna carriers, each first digital representation representing oneantenna carrier, the plurality of first digital representations of theplurality of antenna carriers being frequency multiplexed into thesecond digital representation across the first bandwidth. The methodfurther comprises frequency converting the second digital representationinto radio frequency, and wirelessly transmitting the converted seconddigital representation to the UEs.

According to another aspect, an IRU is provided operable in a basestation system. The base station system comprises the IRU, a BBUconnected to the IRU, and a first RH connected to the IRU via a packetdata network. The first RH is arranged for wireless transmission in RFof a plurality of antenna carriers to UEs. The plurality of antennacarriers are to be transmitted from the first RH at individuallydifferent RFs. The IRU comprises a processor and a memory. The memorycontains instructions executable by said processor, whereby the IRU isoperative for receiving, from the BBU, a plurality of first digitalrepresentations of the plurality of antenna carriers of the first RH,each first digital representation representing one antenna carrier, theplurality of first digital representations being received in a basebandfrequency range. The IRU is further operative for frequency multiplexingthe plurality of first digital representations of the plurality ofantenna carriers into a second digital representation over a firstbandwidth, and transmitting the second digital representation to thefirst RH.

According to another aspect, an RH is provided operable in a basestation system. The RH is arranged for wireless transmission in RF of aplurality of antenna carriers to UEs. The plurality of antenna carriersare to be transmitted from the RH at individually different RFs. Thebase station system comprises the RH, an IRU connected to the RH via apacket data network, and a BBU connected to the IRU. The RH comprises aprocessor and a memory. The memory contains instructions executable bysaid processor, whereby the RH is operative for receiving, from the IRU,a second digital representation in a first bandwidth, the second digitalrepresentation comprising a plurality of first digital representationsof the plurality of antenna carriers, each first digital representationrepresenting one antenna carrier, the plurality of first digitalrepresentations of the plurality of antenna carriers being frequencymultiplexed into the second digital representation across the firstbandwidth. The RH is further operative for frequency converting thesecond digital representation into radio frequency, and for wirelesslytransmitting the converted second digital representation to the UEs.

According to other aspects, computer programs and carriers are alsoprovided, the details of which will be described in the claims and thedetailed description.

Further possible features and benefits of this solution will becomeapparent from the detailed description below.

BRIEF DESCRIPTION OF DRAWINGS

The solution will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIGS. 1a-1c are block diagrams of distributed base station systemsaccording to the prior art.

FIG. 2 is a distributed base station system according to embodiments ofthe invention.

FIG. 3 is a flow chart illustrating a method performed by an IRU,according to possible embodiments.

FIGS. 4-5 are other flow charts illustrating other methods performed byan IRU, according to possible embodiments.

FIG. 6 is a flow chart illustrating a method performed by an RH,according to possible embodiments.

FIGS. 7-8 are other flow charts illustrating other methods performed byan RH, according to possible embodiments.

FIG. 9a is a block diagram of a CPRI Mux of the prior art of FIG. 1a ,in more detail.

FIG. 9b is a block diagram of an IRU of FIG. 2 in more detail, accordingto possible embodiments.

FIG. 10 is another block diagram of an IRU in more detail, according topossible embodiments.

FIG. 11-12 are block diagrams of an IRU according to possibleembodiments.

FIG. 13-14 are block diagrams of an RH, according to possibleembodiments.

DETAILED DESCRIPTION

Briefly described, a cost-efficient and communication-resource efficientbase station system is provided. The base stations system comprises abase band unit, BBU, an intermediate radio unit, IRU, and a number ofradio heads, RH. The BBU provides first digital representations of aplurality of antenna carriers of one RH to the IRU. The IRU frequencymultiplexes the first digital representations into one second digitalrepresentation, wherein the first digital representations aredistributed over a first bandwidth. The first bandwidth may be aninstantaneous bandwidth, IBW. The IRU can perform DFE functionality onthe common second digital representation hereby only needing one DFEfunctionality for all antenna carriers of one RH, alternatively for oneantenna of one RH if the RH has more than one separate antenna. Byletting the IRU perform the DFE functionality instead of the RHs, theRHs can be made more cost-efficient. As there are still digital datatransmitted from the IRU to the RH, a packet data network can be usedfor connecting the IRU with the RHs.

FIG. 2 shows an embodiment of a base station system 200 in which thepresent invention can be used. The base station system 200 comprises anIRU 210, a BBU 230 connected to the IRU 210 via wireline. The basestation system of FIG. 2 further comprises a first RH 221, a second RH222 and a third RH 223 connected to the IRU 210 via a packet datanetwork 240. The first, second a third RHs are arranged for wirelesstransmission in radio frequency, RF, of a plurality of antenna carriersto user equipments, UEs 250. In FIG. 2, the IRU 210 has been shown as anode separate from the BBU 230. However, the IRU 210 might as well be anintegral part of the BBU node 230 as well being a separate node. Thepacket data network may be for example a Layer 2 Ethernet or a Layer 3IP network, or any other packet switched network. When connected in awireless communication network, the BBU is connected to other basestations, e.g. eNodeBs in a 3G/4G network via an X2 interface, and/orthe BBU is connected to other radio access network nodes such as aMobility Management Entity, MME, or Serving Gateway, SGW, in a 3G/4Gnetwork via an S1 interface.

FIG. 3, in conjunction with FIG. 2, shows an embodiment of a methodperformed by an IRU 210 of a base station system 200, the base stationsystem comprising the IRU 210, a BBU 230 connected to the IRU 210, and afirst RH 221 connected to the IRU 210 via a packet data network 240. Thefirst RH 221 is arranged for wireless transmission in radio frequency,RF, of a plurality of antenna carriers to user equipments, UEs 250, theplurality of antenna carriers being transmitted from the first RH atindividually different RFs. The method comprises receiving 302, from theBBU 230, a plurality of first digital representations of the pluralityof antenna carriers of the first RH 221, each first digitalrepresentation representing one antenna carrier, the plurality of firstdigital representations being received in a baseband frequency range.The method further comprises frequency multiplexing 304 the plurality offirst digital representations of the plurality of antenna carriers intoa second digital representation over a first bandwidth, and transmitting308 the second digital representation to the first RH 221.

By frequency multiplexing digital representations of each of a pluralityof antenna carriers for one RH into one common digital representationover a first bandwidth, digital front end functions such as CFR, DPD canbe performed on the common second digital representation instead of oneach of the individual first digital representations. This also makes itpossible to centralize digital front end functions at the IRU instead ofhaving individual digital front-ends at the RHs. This allows for slimmerRHs compared to the RHs handling digital downlink signals used in priorart.

The term “radio head” (RH) is meant to cover the concept of RU as wellas RH. The term “antenna carrier” is to be interpreted as signals sentover a carrier bandwidth from the BBU via the antenna of the RH to theUE. There are normally a plurality of antenna carriers per antenna perRH or at least per RH. The different antenna carriers of one RH aretransmitted at individually different RF bandwidths from the RH to theUE. The antenna carriers are transported in antenna carrier containers,see e.g. CPRI specification V7.0. The antenna carrier couldalternatively be called antenna carrier signals to define that there aresignals that are sent in a carrier bandwidth. From the BBU, a pluralityof first digital representations of different antenna carrier isreceived in a base frequency bandwidth, i.e. baseband, at the IRU. Thefirst bandwidth over which the first digital representations arefrequency multiplexed into a second digital representation may be in abaseband frequency range or in an intermediate frequency range inbetween baseband and RF. The first bandwidth may be an instantaneousbandwidth, also called intermediate bandwidth, IBW. The IBW can be seenas the largest bandwidth that a radio receiver or radio transmitter inthe RH can access without changing the local oscillator. The concept ofIBW is independent of center frequency: If 100 MHz IBW is wanted at theRH, i.e. at radio frequency, RF, range, also 100 MHz IBW is needed at anintermediate frequency in between baseband and RF if an intermediatefrequency is used for the IBW, and also 100 MHz IBW is needed atbaseband if baseband is used for the IBW. At baseband, signals arecomplex with both positive and negative frequencies so the signal willbe from −50 to +50 MHz but the bandwidth is the same. The BBU 230 may beconnected to the IRU 210 via a point-to-point connection, which be awireline connection.

According to an embodiment, in the frequency multiplexing 304, theplurality of antenna carriers are distributed in frequency across thefirst bandwidth according to their individual RFs for transmission fromthe first RH 221 to the UEs. In other words, the plurality of antennacarriers are distributed along the first bandwidth of the second digitalrepresentation in the same frequency relation as they are to have whenbeing transmitted in radio frequency from the first RH. Hereby, thefirst RH does not need to de-multiplex the received plurality of antennacarriers as in prior art. Instead, the first RH can take the receivedsecond representation including the plurality of antenna carriers andjust convert the second representation including the respectivefrequency of each of the plurality of antenna carriers from the IBW intothe RF, and then transmit the frequency-converted antenna carrierswirelessly from the first RH. This simplifies the RHs a lot, which makesthe RHs more cost-efficient, compare to sending individual antennacarriers to the first RH.

FIG. 4 shows embodiments of the method shown in FIG. 3. According to oneembodiment, the method described in FIG. 3 further comprises performing305, crest factor reduction, CFR, and digital pre-distortion, DPD, onthe second digital representation, before the transmission 308 of thesecond digital representation to the first RH. As the CFR and DPD isperformed in the IRU instead of in the RH, the RH can be producedsmaller and lower powered, i.e. to a lower cost than an RH comprisingCFR and DPD functionality. Another benefit is that it may be possible toperform DPD and CFR on the common second digital representation insteadof performing it individually for each antenna carrier at the RH. Abandwidth reduction compression algorithm may be used on the seconddigital representation. The bandwidth reduction compression algorithmmay be an algorithm that does not change the sampling rate such as LPC,if combined with DPD, as the signal on which DPD is to be performedneeds to be 3-5 times oversampled to be correctly performed.

According to another embodiment shown in FIG. 4, the method of FIG. 3further comprises compressing 306 the second digital representation intoa compressed second digital representation. Further, the transmitting308 comprises transmitting the compressed second digital representationto the first RH. The compressed second digital representation has fewerbits than the non-compressed second digital representation. In case CFRand DPD is performed on the second digital representation, thecompression may be performed after CFR and DPD. Hereby, communicationresources in the packet data network are saved.

According to an alternative to the above embodiment, the compressing 306comprises resampling as well as vector quantization and/or transformcoding of the second digital representation. By resampling and then alsovector quantizing and/or performing transform coding onto the resampledsecond digital representation, the bit rate of the transmission to thefirst RH could be reduced forward, for example to reach a level where alower speed Ethernet technology can be used for the packet data network,i.e. a cost-efficient packet data network can be used. A suitableexample of transform coding is Linear Predictive Coding, LPC. Also,noise shaping may be used.

According to another alternative, the compressing 306 comprises a powerspectrum density, PSD, dependent compression of the second digitalrepresentation. Hereby, the bit rate of the transmission to the first RHcan be reduced when data to be sent on the antenna carriers does notfully load the antenna carriers in the first bandwidth. The PSDdependent compression may be an adaptive load dependent compression.

According to another embodiment, which is shown in FIG. 5, the methodfurther comprises receiving 310, from the first RH 221, a digitaltransmitter observation receiver, TOR, signal, the TOR signal being thesecond digital representation frequency-converted into RF and amplifiedby the first RH, and applying 312 the digital TOR signal when performingthe DPD. A TOR circuit in the RH sample and digitize an output signalfrom a power amplifier of the RH. The output signal from the poweramplifier is the second digital representation frequency converted intoRF, DA-converted and amplified by the RH before being sent to therespective antenna for wireless transmission. The sampled and digitizedoutput signal, i.e. the TOR signal, is a signal comprising the wantedoutput plus intermodulation distortion products mainly generated in thepower amplifier. Typically, the TOR needs higher measurement bandwidththan the first bandwidth, e.g. 3 times higher bandwidth. From the TORsignal it is possible to calculate an inverse function of the poweramplifier nonlinearities. This inverse is then applied on the seconddigital representation, after CFR, and this operation is the DPD.Basically, the DPD will amplify strong samples slightly more than weaksamples in order to counteract the PA's characteristic. In prior art,the DPD as well as the power amplifier is in the RH. However, accordingto an embodiment of this invention, the DPD is performed in the IRU. Ascalculating and applying DPD has high computational complexity, the RHcould be simplified by moving the DPD to IRU. The problem is that theTOR is in the RH. By sending a signal comprising the TOR to the IRU, theIRU can perform the DPD. As shown in FIG. 4, the steps of FIG. 5 is tobe performed before the step 305 of performing CFR and DPD on the seconddigital representation, in the embodiment where CFR and DPD areperformed.

According to an alternative of this embodiment, the received digital TORsignal is compressed. By compressing the TOR signal, e.g. by LPC, it ispossible to send the TOR signal on the uplink, i.e. from the RH to theIRU, in Time Division Duplex, TDD, instead of regular uplink signals. Acompression may be necessary as the bandwidth of the uncompressedTOR-signal is often higher than the available bandwidth on the uplink.Further, sending the TOR-signal on the uplink would be an efficientusage of transmission resources as the uplink is not used duringdownlink transmission in TDD mode.

According to another embodiment, the first RH 221 has a first antennaand a second antenna, and a first set of the first digitalrepresentations are representations of antenna carriers of the firstantenna, and a second set of the first digital representations arerepresentations of antenna carriers of the second antenna. Further, thefrequency multiplexing 304 into the second digital representationcomprises frequency multiplexing the first set of the first digitalrepresentations into a primary second digital representation, andfrequency multiplexing the second set of the first digitalrepresentations into a secondary second digital representation. Thetransmitting 308 then comprises transmitting the primary second digitalrepresentation to the first RH 221 and transmitting the secondary seconddigital representation to the first RH. In case the first RH has morethan one antenna, e.g. a first and a second antenna, the first digitalrepresentations of antenna carriers of the first antenna are multiplexedand sent into one second digital representation, which at the first RHis directed to the transmitter of the first antenna. In a similar way,the first digital representations of antenna carriers of the secondantenna are multiplexed and sent into another second digitalrepresentation, which at the first RH is directed to the transmitter ofthe second antenna.

FIG. 6, in conjunction with FIG. 2, describes an embodiment of a methodperformed by an RH 221 of a base station system 200, the RH 221 beingarranged for wireless transmission in radio frequency, RF, of aplurality of antenna carriers to UEs 250. The plurality of antennacarriers are to be transmitted from the RH 221 at individually differentRFs. The base station system comprises the RH 221, an IRU 210 connectedto the RH 221 via a packet data network 240, and a BBU 230 connected tothe IRU 210. The method comprises receiving 402, from the IRU 210, asecond digital representation in a first bandwidth, the second digitalrepresentation comprising a plurality of first digital representationsof the plurality of antenna carriers, each first digital representationrepresenting one antenna carrier, the plurality of first digitalrepresentations of the plurality of antenna carriers being frequencymultiplexed into the second digital representation across the firstbandwidth. The method further comprises frequency converting 408 thesecond digital representation into radio frequency, and wirelesslytransmitting 410 the converted second digital representation to the UEs250.

According to an embodiment, in the received second digitalrepresentation, the plurality of antenna carriers are distributed infrequency along the first bandwidth according to their individual RFsfor transmission from the RH 221 to the UEs.

FIG. 8 describes an embodiment of the method described in FIG. 6.According to the embodiment of FIG. 8, the RH 221 comprises a poweramplifier for amplifying the frequency converted second digitalrepresentation. Further, the method further comprises sampling anddigitizing 412 an output signal from the power amplifier, and sending414 the sampled and digitized output signal to the IRU 210 as a digitaltransmit observation receiver signal, TOR signal, for use by the IRUwhen performing DPD. The output signal from the power amplifier is anamplified version of the received and frequency converted second digitalrepresentation. According to an alternative, the TOR signal iscompressed before it is sent 414 to the IRU.

FIG. 7 shows an embodiment of the method described in FIG. 6. Accordingto the embodiment of FIG. 7, the received second digital representationis a compressed version of an original version of the second digitalrepresentation, the second digital representation being compressedaccording to a compression scheme. Further, the method further comprisesde-compressing 406 the received second digital representation accordingto the compression scheme to obtain a version of the second digitalrepresentation corresponding to the original version.

According to an embodiment, the RH 221 has a first antenna and a secondantenna. Further, the received second digital representation comprises aprimary second digital representation comprising a first set of thefirst digital representations that are representations of antennacarriers of the first antenna, the first set of the first digitalrepresentations being frequency multiplexed into the primary seconddigital representation. The received second digital representationfurther comprises a secondary second digital representation comprising asecond set of the first digital representations that are representationsof antenna carriers of the second antenna, the second set of the firstdigital representations being frequency multiplexed into the secondarysecond digital representation. The method further comprises transportingthe primary second digital representation to the first antenna and thesecondary second digital representation to the second antenna forwireless transmission from the respective first and second antenna tothe UEs.

According to an embodiment and compared to the prior art systems of FIG.1a and 1b , the IRU takes the place of the Mux and HUB, respectively.The IRU hosts the DFE functionality instead of the RH, and the RH onlyprovides fronthaul interfacing and AFE functionality.

According to an embodiment, instead of using an analog interface betweenthe IRU 210 and the RH 221 as in the prior art of FIG. 1c , theinterface is a digital packet based network, such as Ethernet. Andinstead of sending analog versions of the antenna carriers between theIRU and the RH, digital signal representations of antenna carriers aremultiplexed into an IBW that is packetized into e.g. Ethernet frames andsent over the digital packet based network to the RH. It should be notedthat there is an ongoing development of an evolved CPRI, eCPRI thatspecifies packet transport mechanisms of radio signals over packet datanetwork such as Layer 2/Layer 3 Ethernet/IP networks instead of point topoint fibers. This will allow for using eCPRI over the packet datanetwork between the IRU and the RH. eCPRI allows for service diversityand a better utilization of the network.

According to an embodiment, the IRU receives a plurality of base-bandantenna carriers. DFE functionality in the IRU multiplexes the carriersin frequency to their final carrier frequency location in relation toeach other and to the configured power levels in baseband. This compoundof carriers is called the IBW and reflects a copy of what would beradiated from one antenna of an RH on RF, but in baseband. In otherwords, in the IBW, the antenna carriers are a digital version of theanalog signal to be transmitted from the antennas, with the samedistance in frequency between the antenna carriers as they will havewhen transmitted from the antenna, only in baseband instead of in RF. Asthe RH receives the IBW, it only needs to DA convert the IBW, frequencytransform the IBW from baseband to RF and send the transformed DAconverted IBW from its antenna. In case the RH has more than oneantenna, the antenna carriers would be frequency multiplexed intoseparate IBWs per antenna, depending on to which antenna the differentantenna carriers belong.

FIG. 9a shows details of the CPRI Mux 120 of the prior art system shownin FIG. 1a . Antenna carriers, AxCs are received over CPRI from the BBUat a CPRI unit 121. The CPRI unit 121 demultiplexes the AxCs from thecommon CPRI signal into individual AxCs and sends them to individual AxCprocessing units 122 ₁-122 _(n) so that the individual AxCs areprocessed individually by the AxC processing units. The processing maybe compression in downlink and decompression in uplink. The individualAxCs are then packaged into frames by individual AxC packaging units 123₁-123 _(n). A packet switch 124 forwards the packetized antenna carrierstowards the targeted RU where DFE processing takes place. In otherwords, the processing is here per AxC and there will be one frame flowper AxC.

FIG. 9b shows details of an IRU according to embodiments of theinvention. AxCs are received over CPRI from the BBU at a CPRI unit 521.The CPRI unit 521 demultiplexes the AxCs from the common CPRI signalinto individual AxCs. The individual AxCs are then processed by aprocessing unit 522. The processing unit 522 frequency multiplexes theAxCs for a given RH into IBW in complex baseband as an IBW₁ signal. Theindex “1” in IBW₁ signifies one RH, or the first RH. The multiplecarriers for a given RH are configured in power and frequency relationsin the same way as they are to be when transmitted from the RH in RF.The processing unit 522 further performs DFE functions such as DPD andCFR on the IBW signal. The processed IBW signal is compressed in acompression unit 523 into a compressed IBW, IBW*. If there are gaps inthe IBW, it is preferable to use a compression scheme that can utilizethe gaps to reduce the fronthaul bit rate. A mix of e.g. resampling andLPC coding, that may include linear prediction and entropy coding, couldreduce the bitrate to a level where a lower speed Ethernet technologycan be used, e.g. 2.5GBASE-T instead of 5GBASE-T or 10GBASE-T. Also, anadaptive, load dependent compression can reduce the bit rate furtherwhen the traffic does not fully load the carriers in the IBW. The IBWfor each RH is then packaged into a frame flow by a packaging unit 524to be transmitted over the packet network to the given RHs. 1588 syncand/or SyncE can be used to carry synchronization data.

FIG. 10 shows an embodiment of an IRU in more detail. The processingunit 522 receives the individually separated AxCs and frequencymultiplexes the AxCs belonging to the same RH. In case the RH has morethan one antenna, the AxCs belonging to the same antenna of the same RHare frequency multiplexed in a multiplexors 531 ₁-531 _(n) into IBWsignals 532 ₁-532 _(n). Then, DFE functions such as CFR 533 and DPD 534are performed on the IBW signals. The DFE processed IBW signals are thenfed to a compression unit 523 similar to the compression unit of FIG. 9b, for being compressed, and further fed to a packaging unit 524 similarto the packaging unit of FIG. 9b for being packaged into frames beforebeing transmitted to the RH.

FIG. 11, in conjunction with FIG. 2, shows an IRU 210 operable in a basestation system 200. The base station system comprises the IRU 210, a BBU230 connected to the IRU 210, and a first RH 221 connected to the IRU210 via a packet data network 240. The first RH 221 is arranged forwireless transmission in RF of a plurality of antenna carriers to UEs250. The plurality of antenna carriers are to be transmitted from thefirst RH at individually different RFs. The IRU 210 comprises aprocessor 603 and a memory 604. The memory contains instructionsexecutable by said processor, whereby the IRU 210 is operative forreceiving, from the BBU 230, a plurality of first digitalrepresentations of the plurality of antenna carriers of the first RH221, each first digital representation representing one antenna carrier,the plurality of first digital representations being received in abaseband frequency range. The IRU 210 is further operative for frequencymultiplexing the plurality of first digital representations of theplurality of antenna carriers into a second digital representation overa first bandwidth, and transmitting the second digital representation tothe first RH 221.

According to an embodiment, the IRU 210 is operative for, when frequencymultiplexing, distributing the plurality of antenna carriers infrequency across the first bandwidth according to their individual RFsfor transmission from the first RH 221 to the UEs.

According to an embodiment, the IRU 210 is further operative forperforming CFR and DPD on the second digital representation, beforetransmission of the second digital representation to the first RH.

According to another embodiment, the IRU 210 is further operative forreceiving, from the first RH, a digital TOR signal, the TOR signal beingthe second digital representation frequency-converted into RF andamplified by the first RH, and applying the digital TOR signal whenperforming the DPD.

According to an embodiment, the IRU 210 is further operative forcompressing the received digital TOR signal.

According to another embodiment, the IRU 210 is further operative forcompressing the second digital representation into a compressed seconddigital representation, and for transmitting the compressed seconddigital representation to the first RH.

According to another embodiment, the first RH 221 has a first antennaand a second antenna and a first set of the first digitalrepresentations are representations of antenna carriers of the firstantenna and a second set of the first digital representations arerepresentations of antenna carriers of the second antenna. Further, theIRU 210 is operative for frequency multiplexing the first set of thefirst digital representations into a primary second digitalrepresentation and frequency multiplexing the second set of the firstdigital representations into a secondary second digital representation,and for transmitting the primary second digital representation to thefirst RH 221 and transmitting the secondary second digitalrepresentation to the first RH 221.

According to other embodiments, the IRU 210 may further comprise acommunication unit 602, which may be considered to comprise conventionalmeans for communicating with the BBU 230 and with the RHs 221-223. Theinstructions executable by said processor 603 may be arranged as acomputer program 605 stored e.g. in the memory 604. The processor 603and the memory 604 may be arranged in a sub-arrangement 601. Thesub-arrangement 601 may be a micro-processor and adequate software andstorage therefore, a Programmable Logic Device, PLD, or other electroniccomponent(s)/processing circuit(s) configured to perform the methodsmentioned above.

The computer program 605 may comprise computer readable code means,which when run in IRU 210 causes the IRU 210 to perform the stepsdescribed in any of the described embodiments of the IRU 210. Thecomputer program 605 may be carried by a computer program productconnectable to the processor 603. The computer program product may bethe memory 604. The memory 604 may be realized as for example a RAM(Random-access memory), ROM (Read-Only Memory) or an EEPROM (ElectricalErasable Programmable ROM). Further, the computer program may be carriedby a separate computer-readable medium, such as a CD, DVD or flashmemory, from which the program could be downloaded into the memory 604.Alternatively, the computer program may be stored on a server or anyother entity connected to the communication network to which the IRU 210has access via the communication unit 602. The computer program may thenbe downloaded from the server into the memory 604.

FIG. 12, in conjunction with FIG. 2, shows an alternative embodiment ofan IRU 210 operable in a base station system 200. The base stationsystem comprises the IRU 210, a BBU 230 connected to the IRU 210, and afirst RH 221 connected to the IRU 210 via a packet data network 240. Thefirst RH 221 is arranged for wireless transmission in RF of a pluralityof antenna carriers to UEs 250. The plurality of antenna carriers aretransmitted from the first RH at individually different RFs. The IRU 210comprises a receiving module 704 for receiving, from the BBU 230, aplurality of first digital representations of the plurality of antennacarriers of the first RH 221, each first digital representationrepresenting one antenna carrier, the plurality of first digitalrepresentations being received in a baseband frequency range. The IRUfurther comprises a frequency multiplexing module 706 for frequencymultiplexing the plurality of first digital representations of theplurality of antenna carriers into a second digital representation overa first bandwidth, and a transmitting module 708 for transmitting thesecond digital representation to the first RH 221. The IRU 210 mayfurther comprise a communication unit 602 similar to the communicationunit of FIG. 11.

FIG. 13, in conjunction with FIG. 2, shows an RH 221 operable in a basestation system 200. The RH 221 is arranged for wireless transmission inRF of a plurality of antenna carriers to UEs 250. The plurality ofantenna carriers are to be transmitted from the RH 221 at individuallydifferent RFs. The base station system comprises the RH 221, an IRU 210connected to the RH 221 via a packet data network 240, and a BBU 230connected to the IRU 210. The RH 221 comprises a processor 803 and amemory 804. The memory contains instructions executable by saidprocessor, whereby the RH 221 is operative for receiving, from the IRU210, a second digital representation in a first bandwidth, the seconddigital representation comprising a plurality of first digitalrepresentations of the plurality of antenna carriers, each first digitalrepresentation representing one antenna carrier, the plurality of firstdigital representations of the plurality of antenna carriers beingfrequency multiplexed into the second digital representation across thefirst bandwidth. The RH 221 is further operative for frequencyconverting the second digital representation into radio frequency, andfor wirelessly transmitting the converted second digital representationto the UEs 250.

According to an embodiment, the RH 221 comprises a power amplifier foramplifying the frequency converted second digital representation. The RHis further operative for sampling and digitizing an output signal fromthe power amplifier, and sending the sampled and digitized output signalto the IRU 210 as a TOR signal, for use by the IRU when performing DPD.

According to another embodiment, the RH 221 is further operative forcompressing the TOR signal before sending the TOR signal to the IRU.

According to another embodiment the received second digitalrepresentation is a compressed version of an original version of thesecond digital representation, the second digital representation beingcompressed according to a compression scheme. Further, the RH isoperative for de-compressing the received second digital representationaccording to the compression scheme to obtain a version of the seconddigital representation corresponding to the original version.

According to other embodiments, the RH 221 may further comprise acommunication unit 802, which may be considered to comprise conventionalmeans for communication with the IRU 210 as well as for wirelesscommunication with UEs wirelessly connected to the RH. The communicationunit 802 may for this reason comprise transmitting units fortransmitting wireless signals and receiving units for receiving wirelesssignals. The instructions executable by said processor 803 may bearranged as a computer program 805 stored e.g. in said memory 804. Theprocessor 803 and the memory 804 may be arranged in a sub-arrangement801. The sub-arrangement 801 may be a micro-processor and adequatesoftware and storage therefore, a Programmable Logic Device, PLD, orother electronic component(s)/processing circuit(s) configured toperform the actions and/or methods mentioned above.

The computer program 805 may comprise computer readable code means,which when run in the RH 221 causes the RH to perform the stepsdescribed in any of the described embodiments of the RH. The computerprogram 805 may be carried by a computer program product connectable tothe processor 803. The computer program product may be the memory 804.The memory 804 may be realized as for example a RAM (Random-accessmemory), ROM (Read-Only Memory) or an EEPROM (Electrical ErasableProgrammable ROM). Further, the computer program may be carried by aseparate computer-readable medium, such as a CD, DVD or flash memory,from which the program could be downloaded into the memory 804.Alternatively, the computer program may be stored on a server or anyother entity connected to the communication network to which the RH hasaccess via the communication unit 802. The computer program may then bedownloaded from the server into the memory 804.

FIG. 14, in conjunction with FIG. 2, shows an alternative embodiment ofan RH 221 operable in a base station system 200. The RH 221 is arrangedfor wireless transmission in RF of a plurality of antenna carriers toUEs 250. The plurality of antenna carriers are to be transmitted fromthe RH 221 at individually different RFs. The base station systemcomprises the RH 221, an IRU 210 connected to the RH 221 via a packetdata network 240, and a BBU 230 connected to the IRU 210. The RH 221comprises a receiving module 904 for receiving, from the IRU 210, asecond digital representation in a first bandwidth, the second digitalrepresentation comprising a plurality of first digital representationsof the plurality of antenna carriers, each first digital representationrepresenting one antenna carrier, the plurality of first digitalrepresentations of the plurality of antenna carriers being frequencymultiplexed into the second digital representation across the firstbandwidth. The RH 221 further comprises a frequency converting module906 for frequency converting the second digital representation intoradio frequency, and a transmitting module 908 for wirelesslytransmitting the converted second digital representation to the UEs 250.

The present invention may be used in any radio access technology and onantenna carriers of any radio access technology, such as Global Systemfor Mobile communication, GSM, Wideband Code Division Multiple Access,WCDMA, Long Term Evolution, LTE, Next Evolution, NE.

Although the description above contains a plurality of specificities,these should not be construed as limiting the scope of the conceptdescribed herein but as merely providing illustrations of someexemplifying embodiments of the described concept. It will beappreciated that the scope of the presently described concept fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the presently described concept isaccordingly not to be limited. Reference to an element in the singularis not intended to mean “one and only one” unless explicitly so stated,but rather “one or more.” All structural and functional equivalents tothe elements of the above-described embodiments that are known to thoseof ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed hereby. Moreover, it is notnecessary for an apparatus or method to address each and every problemsought to be solved by the presently described concept, for it to beencompassed hereby. In the exemplary figures, a broken line generallysignifies that the feature within the broken line is optional.

1. A method performed by an intermediate radio unit (IRU) of a basestation system, the base station system comprising the IRU, a basebandunit, (BBU) connected to the IRU, and a first radio head (RH) connectedto the IRU via a packet data network, the first RH being arranged forwireless transmission in radio frequency (RF) of a plurality of antennacarriers to user equipments (UEs), the plurality of antenna carriersbeing transmitted from the first RH at individually different RFs, themethod comprising: receiving, from the BBU, a plurality of first digitalrepresentations of the plurality of antenna carriers of the first RH,each first digital representation representing one antenna carrier, theplurality of first digital representations being received in a basebandfrequency range; frequency multiplexing the plurality of first digitalrepresentations of the plurality of antenna carriers into a seconddigital representation over a first intermediate bandwidth, wherein inthe frequency multiplexing, the plurality of antenna carriers aredistributed in frequency across the first intermediate bandwidthaccording to their individual RFs for transmission from the first RH tothe UEs, so that the plurality of antenna carriers are distributed alongthe first intermediate bandwidth in the same frequency relation as theyare to have when being transmitted in RF from the first RH; andtransmitting the second digital representation to the first RH. 2.(canceled)
 3. The method of claim 1, further comprising: performingcrest factor reduction, CFR, and digital pre-distortion (DPD) on thesecond digital representation, before the transmission of the seconddigital representation to the first RH.
 4. The method of claim 3,further comprising: receiving, from the first RH, a digital TransmitterObservation Receiver (TOR) signal, the TOR signal being the seconddigital representation frequency-converted into RF and amplified by thefirst RH, and applying the digital TOR signal when performing the DPD.5. The method of claim 4, wherein the received digital TOR signal iscompressed.
 6. The method of claim 1, further comprising: compressingthe second digital representation into a compressed second digitalrepresentation, and wherein the transmitting comprises transmitting thecompressed second digital representation to the first RH.
 7. The methodof claim 6, wherein the compressing comprises resampling as well asvector quantization and/or transform coding of the second digitalrepresentation.
 8. The method of claim 6, wherein the compressingcomprises a power spectrum density, PSD, dependent compression of thesecond digital representation.
 9. The method of claim 1, wherein thefirst RH has a first antenna and a second antenna and a first set of thefirst digital representations are representations of antenna carriers ofthe first antenna and a second set of the first digital representationsare representations of antenna carriers of the second antenna, andwherein the frequency multiplexing into the second digitalrepresentation comprises frequency multiplexing the first set of thefirst digital representations into a primary second digitalrepresentation and frequency multiplexing the second set of the firstdigital representations into a secondary second digital representation,and wherein the transmitting comprises transmitting the primary seconddigital representation to the first RH and transmitting the secondarysecond digital representation to the first RH.
 10. A method performed bya radio head (RH) of a base station system, the RH being arranged forwireless transmission in radio frequency (RF) of a plurality of antennacarriers to user equipments (UEs), the plurality of antenna carriersbeing transmitted from the RH at individually different RFs, the basestation system comprising the RH, an intermediate radio unit (IRU)connected to the RH via a packet data network, and a baseband unit (BBU)connected to the IRU, the method comprising: receiving, from the IRU, asecond digital representation in a first intermediate bandwidth, thesecond digital representation comprising a plurality of first digitalrepresentations of the plurality of antenna carriers, each first digitalrepresentation representing one antenna carrier, the plurality of firstdigital representations of the plurality of antenna carriers beingfrequency multiplexed into the second digital representation across thefirst intermediate bandwidth, wherein in the received second digitalrepresentation, the plurality of antenna carriers are distributed infrequency along the first intermediate bandwidth according to theirindividual RFs for transmission from the RH to the UEs so that theplurality of antenna carriers are distributed along the firstintermediate bandwidth in the same frequency relation as they are tohave when being transmitted in RF from the first RH; frequencyconverting the second digital representation into radio frequency; andwirelessly transmitting the converted second digital representation tothe UEs.
 11. (canceled)
 12. The method of claim 10, wherein the RHcomprises a power amplifier for amplifying the frequency convertedsecond digital representation, and the method further comprises:sampling and digitizing an output signal from the power amplifier; andsending the sampled and digitized output signal to the IRU as a digitalTOR signal, for use by the IRU when performing digital pre-distortion(DPD).
 13. The method of claim 12, wherein the TOR signal is compressedbefore it is sent to the IRU.
 14. The method of claim 10, wherein thereceived second digital representation is a compressed version of anoriginal version of the second digital representation, the seconddigital representation being compressed according to a compressionscheme, the method further comprising: de-compressing the receivedsecond digital representation according to the compression scheme toobtain a version of the second digital representation corresponding tothe original version.
 15. The method of claim 9, wherein the RH has afirst antenna and a second antenna, and wherein the received seconddigital representation comprises a primary second digital representationcomprising a first set of the first digital representations that arerepresentations of antenna carriers of the first antenna, the first setof the first digital representations being frequency multiplexed intothe primary second digital representation, and a secondary seconddigital representation comprising a second set of the first digitalrepresentations that are representations of antenna carriers of thesecond antenna, the second set of the first digital representationsbeing frequency multiplexed into the secondary second digitalrepresentation, the method further comprising transporting the primarysecond digital representation to the first antenna and the secondarysecond digital representation to the second antenna for wirelesstransmission from the respective first and second antenna to the UEs.16. An intermediate radio unit (IRU) operable in a base station system,the base station system comprising the IRU, a baseband unit (BBU)connected to the IRU, and a first radio head (RH) connected to the IRUvia a packet data network, the first RH being arranged for wirelesstransmission in radio frequency (RF) of a plurality of antenna carriersto user equipments (UEs), the plurality of antenna carriers are to betransmitted from the first RH at individually different RFs, the IRUcomprising: a processor; and a memory, said memory containinginstructions executable by said processor, wherein the IRU is operativefor: receiving, from the BBU, a plurality of first digitalrepresentations of the plurality of antenna carriers of the first RH,each first digital representation representing one antenna carrier, theplurality of first digital representations being received in a basebandfrequency range; frequency multiplexing the plurality of first digitalrepresentations of the plurality of antenna carriers into a seconddigital representation over a first intermediate bandwidth, wherein, inthe frequency multiplexing, distributing the plurality of antennacarriers in frequency across the first intermediate bandwidth accordingto their individual RFs for transmission from the first RH to the UEs,so that the plurality of antenna carriers are distributed along thefirst intermediate bandwidth in the same frequency relation as they areto have when being transmitted in RF from the first RH; and transmittingthe second digital representation to the first RH. 17-22. (canceled) 23.A computer program comprising computer readable code means to be run inan intermediate radio unit (IRU) of a base station system, the basestation system comprising the IRU, a base band unit (BBU) connected tothe IRU, and a first radio head (RH) connected to the IRU via a packetdata network, the first RH being arranged for wireless transmission inradio frequency (RF) of a plurality of antenna carriers to userequipments (UEs), the plurality of antenna carriers being transmittedfrom the first RH at individually different RFs, which computer readablecode means when run in the IRU causes the IRU to perform the method ofclaim
 1. 24. (canceled)
 25. A radio head (RH) operable in a base stationsystem, the RH being arranged for wireless transmission in radiofrequency (RF) of a plurality of antenna carriers to user equipments(UEs), the plurality of antenna carriers are to be transmitted from theRH at individually different RFs, the base station system comprising theRH, an intermediate radio unit (IRU) connected to the RH via a packetdata network, and a baseband unit (BBU) connected to the IRU, the RHcomprising: a processor; and a memory, said memory containinginstructions executable by said processor, wherein the RH is operativefor: receiving, from the IRU, a second digital representation in a firstintermediate bandwidth, the second digital representation comprising aplurality of first digital representations of the plurality of antennacarriers, each first digital representation representing one antennacarrier, the plurality of first digital representations of the pluralityof antenna carriers being frequency multiplexed into the second digitalrepresentation across the first intermediate bandwidth, wherein in thereceived second digital representation, the plurality of antennacarriers are distributed in frequency along the first intermediatebandwidth according to their individual RFs for transmission from the RHto the UEs so that the plurality of antenna carriers are distributedalong the first intermediate bandwidth in the same frequency relation asthey are to have when being transmitted in RF from the first RH;frequency converting the second digital representation into radiofrequency; and wirelessly transmitting the converted second digitalrepresentation to the UEs.
 26. (canceled)
 27. (canceled)
 28. (canceled)29. A computer program comprising computer readable code to be run in aradio head (RH) of a base station system, the RH being arranged forwireless transmission in radio frequency (RF) of a plurality of antennacarriers to user equipments (UEs), the plurality of antenna carriersbeing transmitted from the RH at individually different RFs, the basestation system comprising the RH, an intermediate radio unit (IRU)connected to the RH via a packet data network, and a baseband unit (BBU)connected to the IRU, which computer readable code when run in the RHcauses the RH to perform the method of claim
 10. 30. (canceled) 31.(canceled)
 32. (canceled)